This invention relates in general to the conversion of carbonaceous material containing metallic components into useful products such as a battery electrolyte.
Because of its relatively low heat content and atmospheric polluting effect as a solid fuel, low grade coals have not been fully exploited. More recently, however, greater interest has been generated in utilizing low grade coals as a substitute source of processed fuels and for non-fuel products. The use of lignite coal, for example, as a liquid extract source for battery electrolyte, is disclosed in U.S. Pat. No. 2,838,429 to Sanders. According to the Sanders patent, ground lignite coal is reached with nitric acid and a dried residue reaction product chemically oxidized to produce an acidic liquid suitable as an electrolyte for storage batteries. Treatment with other chemicals in several different steps in addition to treatment with nitric acid was required according to the Sanders patent in order to obtain a suitable liquid extract.
The use of nitric acid as an ingredient of aqua regia to dissolve metallic compounds in ores and other metal-bearing materials is also well known. The oxidizing power of the nitric acid and its effect on reactions that occur when material being treated is dissolved in the aqua regia, is also well known. This oxidizing power is precisely controlled by modifying the pH value of the aqua regia solution according to U.S. Pat. No. 3,865,507, to Brug et al, so as to regulate the reaction inhibiting effect of the nitric acid and enable precipitation of a solid product by the addition of reducing agents. Such use of aqua regia is, however, restricted to the recovery of metallic gold as disclosed in the Brug et al patent.
The use of low grade coal having metallic component impurities presents a special problem in producing a liquid extract because the presence of such impurities in the extract is detrimental to its use as a battery electrolyte. It is therefore an important object of the present invention to provide a relatively simple and inexpensive method of treating carbonaceous material to produce a liquid extract free of metallic components. Additional objects of the invention include the recovery of useful solid residues containing metallic components in greater concentration and gaseous products.